Other Comprehensive (Loss) Income - Components Reclassified from AOCI to Earnings (Details) - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Pensions and other postretirement benefits
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss to net income, gross	$ 2,445	$ (5,035)	$ 6,294
Tax effects of amounts reclassified from accumulated other comprehensive loss to net income	(25)	(348)	(99)
Amounts reclassified from accumulated other comprehensive loss to net income, net	2,420	(5,383)	6,195
Actuarial loss
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss to net income, gross	3,111	3,238	2,513
Amortization of prior service cost (credit)
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss to net income, gross	(666)	(666)	(667)
Deferred income tax benefit
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss to net income, gross	0	(7,607)	4,448
Derivatives
Reclassification Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from accumulated other comprehensive loss to net income, gross	3,331	1,899	1,818
Tax effects of amounts reclassified from accumulated other comprehensive loss to net income	0	(399)	(382)
Amounts reclassified from accumulated other comprehensive loss to net income, net	$ 3,331	$ 1,500	$ 1,436